That's pronounced "day-z", by the way, not "daze". Or I guess "day zed" if you're British? Maybe? I don't know.
Anyway, DayZ is mod currently in development for Arma II (though due to its popularity the devs have said it may become a full standalone game). It's an open world multiplayer post-apocalyptic zombie survival simulation. Each server can support up to around 50 players. The world in the game is huge
. The game features permanent death, meaning once your current character is dead, they stay dead. There is some persistence to the game in that you can take your gear from one server to another.
I'm going to shut up about the game now since I've never actually played it and if I say anymore I run the risk of totally misrepresenting the game. I suppose I'll let DayZ speak for itself.
These first two videos chronicle a small group doing their best to survive. Think of it as half an episode of The Walking Dead or something. Also, the mod is still in early alpha so you'll have to excuse any jank you see.
This video is an installation guide for anyone super interested.
As a bonus, a fourth video featuring Arnold Schwarzenneger playing DayZ.